Label-free lipid contrast imaging using non-contact near-infrared photoacoustic remote sensing microscopy

Abstract

Histopathology of lipid-rich tissues is often a difficult endeavor, owing to the limited tissue processing workflows that can appropriately preserve tissue while keeping fatty deposits intact. Here, we present the first usage of near-infrared (NIR) photoacoustic remote sensing (PARS) to achieve imaging contrast from lipids without the need for exogenous stains or labels. In our system, the facile production of 1225 nm excitation pulses is achieved by the stimulated Raman scattering of a 1064 nm source propagating through an optical fiber. PARS-based detection is achieved by monitoring the change in the scattering profile of a co-aligned 1550 nm continuous-wave interrogation beam in response to absorption of the 1225 nm light by lipids. Our non-contact, reflection-mode approach can achieve a FWHM resolution of up to 0.96 µm and signal-to-noise ratios as high as 45 dB from carbon fibers and 9.7 dB from a lipid phantom. NIR-PARS offers a promising approach to image lipid-rich samples with a simplified workflow.

Three-dimensional virtual histology in unprocessed resected tissues with photoacoustic remote sensing (PARS) microscopy and optical coherence tomography (OCT)

“…More excitation wavelengths would expand the chromophore specific absorption contrast. This may provide visualizations of biomolecules such as lipids, collagen, heme proteins and more 15 , 19 , 28 , 43 .…”

Three-dimensional virtual histology in unprocessed resected tissues with photoacoustic remote sensing (PARS) microscopy and optical coherence tomography

“…More excitation wavelengths would expand the chromophore specific absorption contrast. This may provide visualizations of biomolecules such as lipids, collagen, heme proteins and more 15,19,28,39 .…”

“…PA offers chromophore specific visualizations by leveraging the unique optical absorption spectra of biomolecules. This has been applied to selectively image DNA/RNA, hemoglobin, melanin, lipids, collagen, and more 14,17,[27][28][29][30][31] . These unique chromophore specific visualizations position PA as a potentially powerful tool for label-free histological imaging 14,15 .…”

Fiber-based photoacoustic remote sensing microscopy and spectral-domain optical coherence tomography with a dual-function 1050-nm interrogation source

“…Previous reports on PARS imaging predominantly used a 1310-nm interrogation wavelength, 13 , 14 , 16 with a single exception involving 1550-nm interrogation. 17 Therefore, we elected to adopt this 1310-nm interrogation wavelength in our initial multimodal system given that 1050-nm PARS interrogation had not been investigated. Hence, the system required the use of three distinct light sources: the 1310-nm PARS interrogation source, a 1050-nm low-coherence OCT source, and a 532-nm pulsed excitation laser.…”